Preheat the oven to 180°C (160°C fan oven) mark 4. Line a 12 hole muffin tin with paper muffin cases.,Sift the flour, bicarbonate de soda and slat into a large mixing bowl and put to one side.,______,Add this to the flour mixture, with the chocolate chips. Stir gently, using only a few strokes, until the flour is only just incorporated - do not over-mix. The mixture should be lumpy. Spoon the mixture equally into the paper cases, half-filling them, and sprinkle with brown sugar and chocolate chips.,Bake for 20 minutes or until the muffins are well risen and golden. Transfer to a wire rack and leave cool.